Electrode coil and method



Dec. 27, 1966 T, H, HElNE 3,294,125

ELECTRODE COIL AND METHOD Filed Nov. 14, 1963 s sheets-'sheet 1 WITNESSES INVENTOR 2am JVM Thomas H. Heine @Y0/QM ATTORNEY Dec. 27, 1966 y T. H. HEINE ELECTRODE COIL AND METHOD 5 Sheets-Sheet 2 Filed NOV. 14. 1963 Dec. 27, 1966 T. H, HEINE ELECTRODE COIL AND METHOD 5 Sheds-Sheet I3 Filed Nov. 14, 1963 United States Patent O 3,294,125 ELECTRODE COIL AND METHOD Thomas H. Heine, Cedar Grove, NJ., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 14, 1963, Ser. No. 323,741 Claims. (Cl. 140-71.5)

This invention relates to electrodes for electric discharge devices and, more particularly, to electrode coils for high-wattage fluorescent lamps and to the method for making such coils.

Flourescent lamp cathodes and particularly those for so-called rapid and instant start ylamps normally include a fine wire winding that heats up rapidly and yet has an overall structure which is sufficiently massive to avoid localized overheating and sputtering. In addition, such coils must be capable of retaining a sufficient amount of electron emissive material to enable the lamps 4to have a long, useful life.

In the past, such fluorescent lamps have utilized an electrode which comprises a fine wire wound around a heavier core wire, with the resultant composite wire wound into the form of a coil. This coil is, in turn, wound into a still larger coil to provide what is known in the art as a triple-wound electrode coil. In this construction, only the fine wire overwinding is formed as a triple coil and the heavier mandrel wire is formed into a double or coiled-coil. The desired large carrying capacity for electron emissive material is obtained by pairing a temporary filler wire with a core or mandrel wire before the fine wire winding is applied and, after the subsequent coiling operations have been completed, the filler wire is chemically dissolved and removed from the soil struct-ure. Thus the line wire is loosely draped around the core or mandrel wire, resulting in a basket-like structure which can contain avery large amount of emission material. Such a triple-wound electrode is disclosed in U.S. Patent No. 2,306,925, dated December 29, 1942. In copending application Serial No. 165,884, filed January l2, 1962, now Patent No. 3,247,699, and owned by the present assignee, is disclosed a triple-wound electrode which is fabricated in such a manner that the fine wire is protected against attening or abrasion during fabrication.

With the foregoing electrode coil structures, some manufacturing difficulties have been encountered since the fine overwind wire is held only Lloosely by the primary tungsten mandrel. As a result, the overwind may tend to slip back from the end of the coil leg and expose the primary mandrel, or the overwind may slip off the end of the filament leg to form a burr. This promotes tangling and so-called shrinkage, since if the mandrel is exposed, the fine wire may fail t0 reach into the mount clamps for securing the lamentary electrode to the support wires of the lamp stem.

It is the general object of the present invention to provide a method of making electrode coils wherein the line overwind Wire is held in position on the tungsten mandrel.

It is another object to provide a method for making electrode coils wherein any tendency for movement between the fine overwind wire and the surrounded tungsten mandrel is retarded.

A further object is to provide an electrode, especially for liuorescent lamps, wherein manufacturing costs are materially reduced by minimizing shrinkage, and quality of the product is improved by insuring that the ends of the filament which are clamped into position also make proper electrical contact with the lead-in and support wires of the stem mount portion of the lamp.

The aforesaid objects of the invention, and other objects which will become apparent as the description proceeds, are achieved by providing an electrode coil for an electric-discharge Alamp in which a fine wire overwinding of predetermined low pitch is carried on a mandrel, with a spacing between a longitudinal portion of the mandrel and the overwinding. T o hold the overwinding in place on the mandrel, a fine wire coil of predetermined high pitch is disposed in the spacing between-the mandrel and the turns of lthe overwinding and in contacting relationship with both, in order to retard relative movement between the mandrel and the overwinding. In making such an electrode coil, a fine wire is wound with a high pitch about a first mandrel. The resulting line-wirecoiled mandrel is then placed parallel to and in contacting relationship with a second mandrel. An overwind of a second line wire is wound as a low pitch coil completely about the first-wire-coiled mandrel and the parallel second mandrel, in order to form an overwound composite. After the overwound composite is in its desired electrode coil conguration and is set, the first mandrel is dissolved to leave the first wire coil engaging both the second mandrel and the second wire coil to hold the second wire coil in position about the second mandrel. Such an electrode coil structure can be -utilized in a coiledcoil configuration or in a triple coil configuration.

For a better understanding of the invention reference should be had to lthe accompanying drawings wherein:

FIGURE 1 is a perspective view of a portion of a mount for a lhigh wattage fiuorescent lamp which utilizes the electrode coil of the present invention;

FIGURE 2 is an enlarged fragmentary elevational view showing the initial coiling operation of the present invention;

FIGURE 3 is a cross sectional view taken on the [line III-III of FIG. 2, in the direction of the arrows;

FIG. 4 is a fragmentary elevational view of the present electrode coil wherein the overwind filament is held in place on the primary mandrel by a high pitch fine wire coiling, after the forming mandrel has been removed;

FIG. 5 is a cross sectional View taken on the line V-V of FIG. 4, in the direction of the arrows;

FIG. 6 is a fragmentary view, shown partly in section, illustrating the fabrication of a coiled-coil electrode;

FIG. 7 is a fragmentary view showing a coiled-coil electrode after the forming mandrels are dissolved; and

FIG. 8 is a fragmentary View showing the general construction for a triple-coil electrode fabricated in accordance with the present invention.

With specific reference to the form of the invention illustrated in the drawings, in FIG. l is shown an electrode mount 10 for a super-high-output, rapid-start fluorescent lamp. The electrode mount comprises the customary glass flare tube 12 sealed at the press portion thereof about a pair of lead-in and support conductors 14 which are formed into clamps 16 to engage the respective ends of the finished electrode 18. If the electrode is of a triple-coil construction, as shown in FIG. 8, the turns of the minor coils are impregnated with and carry electron emission material such as a mixture of barium, strontium and calcium oxides, and such emission materials are well known. If the electrode is of a coiled-coil construction, such as shown in FIG. 7, either the minor coil can carry the electron emission material or the entire electrode can be impregnated with electron emission material to form a so-called barrelless coil wherein the turns of the major coil are completely bridged by electron emission material. As is customary with such lamps, a heat-deliecting shield 20 is mounted on the press 22. The ends of each of the lead-in wires 14 have afiixed thereto enlarged anodes 24 which are disposed on each side of the electrode 18.

In forming the present electrode coil, as shown in FIGS. 2 and 3, a first fine wire 26, which is formed of selected refractory metal such as tungsten, is coiled with a high pitch about a first removable mandrel 28, which is preferably formed of molybdenum. The resulting firstwre-coiled mandrel is placed parallel to and contacting a second or permanent mandrel 30, which is preferably formed of tungsten. A second fine wire 32, preferably formed of tungsten is then Wound as a low pitch coil completely about and contacting the fine-wire coiled mandrel 28 and the parellel second mandrel 30 to form an overwound composite, as shown in detail in FIGS. 2 and 3. It may be desirable, in accordance with the aforementioned copending application Serial No. 165,884, to place a molybdenum buffer wire 34 between the individual turns of the tungsten wire 32, in order to protect this fine wire during the coiling and to establish the proper low pitch.

In accordance with the present invention, as shown in FIG. 6, the wire composite as shown in FIGS. 2 and 3 is wound about a third mandrel 36, preferably formed of molybdenum. After this Winding operation, the formed electrode coil may, if desired, be wound about a steel mandrel (not shown) after which the steel mandrel is withdrawn to form triple wound electrode coil. Such a finished coil 38, with all forming mandrels removed and dissolved is shown in FIG. 8.

If it is desired to form a coiled-coil electrode, the molybdenum mandrels 28 and 36 are dissolved from the composite coil construction, as shown in FIG. 6, in order to provide a coiled-coil electrode 40 as shown in FIG. 7. This dissolving operation also dissolves the buffer Wire 34, if such wire is used. If it is desired to fabricate a triple-coiled electrode the molybdenum mandrels are not dissolved until the triple coil is actually formed, in order to provide the triple-wound electrode coil 38, as shown in FIG. 8.

As a specific example, the molybdenum mandrel 28 has a diameter of 8 mils and the fine tungsten wire 26 has a diameter of l mil and is wound on the molybdenum mandrel 28 with a high pitch of 40 turns per inch. The tungsten mandrel 30 has a diameter of approximately 5.3 mils. The fine overwind tungsten filament 32 has a diameter of 1 mil and a pitch of 380 turns per inch. If the buffer wire 34 is used, it is formed of molybdenum and has a diameter of 1.5 mils. The molydenum mandrel 36, as shown in FIG. 6, has a diameter of 13 mils. If a triple-wound coil is to be formed, as shown in FIG. 8, the composite mandrel and coiling as shown in FIG. 6 is Wound upon a 50 mil diameter steel mandrel in accordance with conventional processing. The resulting triplewound coil has an inner peripheral diameter of 50 mils. After formation of the triple-wound electrode coil, the steel mandrel is simply withdrawn from -the formed triple coil.

Preparatory to dissolving the molybdenum mandrels 28 and 36, it is desirable to anneal or set the tungsten filament windings before the supporting molybdenum mandrels are dissolved, in order to relieve strains and prevent the very fine filament Wires from distorting. Such a setting procedure is well known in the art and is accomplished by heating the wound electrode coil in a non-oxidizing atmosphere such as hydrogen at a temperature of from 1050" C. to 1500 C. for a period of about 6 minutes. Thereafter the set electrode coil is placed into a solution which comprises parts of nitric acid, 6 parts of sulfuric acid and 2.5 parts of water. This dissolves the molybdenum supporting mandrels 28 and 36 and the buffer wire 34, if such is used, to form the electrode coils which are shown in FIGS. 4, 5, 7 and 8, depending upon what coil construction is preferred. The foregoing specific example is subject to considerable modification with respect to the specific values which are given.

The finished electrode coil is not subject to tangling with other coils or to movement of the overwind with respect to the supporting tungsten mandrel 30, since the high pitch tungsten coil 26 contacts both the tungsten mandrel 30 and the fine overwind 32 in order to retard any relative movement therebetween and to prevent tangling with other coils. For the specific example as given hereinbefore, approximately 70% of the total turns of the fine overwind coil are contacted by the high pitch holding coil 26. In addition, the high pitch coil 26 occupies very little of the spacing which is provided between the overwind coil 32 and the tungsten mandrel, thus leaving ample capacity for the subsequent filling with electron emission material in order to complete fabrication of the electrode.

It will be recognized that the objects of the invention have been achieved by providing a method for fabricating an electrode coil which is not subject to tangling or distortion during fabrication and subsequent handling. This, in turn, reduces costs and assures that the coil is always properly fabricated.

While a best example of the invention has been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

I claim as my invention:

1. The method of making a coiled wire and mandrel suitable for use as an electrode coil for an electric-discharge device, which method comprises:

(a) Winding a first wire as a coil about a first mandrel;

(b) placing the resulting first-wire-coiled mandrel parallel to and adjacent a second mandrel;

(c) overwinding a second wire as a coil completely about said first-wire-coiled mandrel and said parallel and adjacent second mandrel to form an overwound composite; and

(d) when said overwound composite is in its desired electrode coil configuration, removing said rst mandrel while leaving said first Wire coil to hold said second wire coil in position about said second mandrel.

2. The method of making a coiled wire and mandrel suitable for use as an electrode coil for an electric discharge device, which method comprises:

(a) winding a first wire of selected refractory metal as a coil about a first mandrel which differs in composition from the first wire;

(b) placing the resulting frst-wire-coiled mandrel parallel to and contacting a second mandrel of said selected refractory metal;

(c) overwinding a second wire of said selected refractory metal as a coil completely about and contacting said first-wire-coiled mandrel and said parallel second mandrel t-o form an overwound composite; and

(d) when said overwound composite is in its desired electrode coil configuration and is set, removing said first mandrel while leaving said first wire coil engaging both said second mandrel and said second wire coil to hold said second wire coil in position about said second mandrel.

3. The method of making a coiled wire and mandrel suitable for use as an electrode coil for an electric discharge device, which method comprises:

(a) winding a first fine wire as a high pitch coil about a first mandrel;

(b) placing the resulting first-wire-coiled mandrel parallel to and in contact with a second mandrel which differs in composition from said first wire;

(c) overwinding a second fine wire as a low pitch coil completely about and contacting said first-wire-coiled mandrel and said parallel second mandrel to form an overwound composite; and

(d) when said overwound composite is in its desired electrode coil configuration and is set, removing said first mandrel while leaving said high pitch first wire coil engaging both said second mandrel and said low pitch second wire coil to hold said second wire coil in position about said second mandrel.

4. The method of making a coiled wire and mandrel suitable for use as an electrode coil for an electric discharge device, which method comprises:

(a) winding a first fine wire of selected refractory metal as a high pitch coil about a rst mandrel which differs in composition from the first wire;

(b) placing the resulting first-wire-coiled mandrel parallel to and contacting a second mandrel of said selected refractory metal;

(c) overwinding a second fine wire of said refractory metal as a low pitch coil completely about and contacting said first-wire-coiled mandrel and said parallel second mandrel to form an overwound composite; and

(d) when said overwound composite is in its desired electrode coil configuration and is set, dissolving said first mandrel while leaving said first wire coil engaging both said second mandrel and said second wire coil to hold said second wire coil in position about said second mandrel.

5. The method of making a coiled wire and mandrel suitable for use as an electrode coil for an electric discharge device, which method comprises:

(a) winding a first tine tugsten wire as a high pitch coil about a molybdenum mandrel (b) placing the resulting wire-coiled molybdenum mandrel parallel to and adjacent a tungsten mandrel which has a smaller diameter than said molybdenum mandrel;

(c) overwinding a second fine tungsten wire as a coil completely about said wire-coiled molybdenum mandrel and said parallel tungsten mandrel to form an overwound composite; and

(d) when said overwound composite is in its desired electrode coil configuration and is set, dissolving said molybdenum mandrel while leaving said first wire coil engaging both said tungsten mandrel and the inner periphery of said second wire coil to hold said second wire coil in position about said tugsten mandrel.

6. The method as specified in claim 5, wherein a ne molybdenum Wire of predetermined diameter is wound with said second tungsten wire between individual turns thereof to control the pitch of the formed second wire coil, and said fine molybdenum wire is dissolved with said molybdenum mandrel.

7. The method of forming a coiled wire and mandrel suitable for use as an electrode coil for an electric discharge device, which method comprises:

(a) Winding a first wire of predetermined fine diameter as a coil of predetermined low pitch about a first mandrel having a predetermined diameter;

(b) placing the resulting first-wire-coiled mandrel parallel to and in contact with a second mandrel having a predetermined diameter;

(c) overwinding a second wire of predetermined ne diameter as a coil of predetermined high pitch completely about said first-wire-coiled mandrel and said parallel second mandrel to form an overwound composite;

(d) winding said overwound composite as a coil of predetermined pitch about a third mandrel of predetermined large diameter; and

(e) when said overwound composite as coiled on said third mandrel is in its desired electrode coil configuration and is set, dissolving said first mandrel and said third mandrel while leaving said first wire coil 5 engaging both said second mandrel and said second wire coil to hold said second wire coil in position on said second mandrel.

8. The method as specified in claim 7, wherein said first wire, said second wire and said second mandrel are formed of tungsten, and said first mandrel and said third mandrel are formed of molybdenum.

9. The method as specified in claim 8, wherein a fine molybdenum wire of predetermined diameter is wound with said second wire between individual turns thereof to control the pitch of the formed second wire coil, and said fine molybdenum wire is dissolved With said first mandrel and said third mandrel.

10. The method of forming a coiled wire and mandrel suitable for use as an electrode coil for an electric discharge device, which method comprises:

(a) winding a first wire of predetermined fine diameter as a coil of predetermined low pitch about a rst mandrel having a predetermined diameter;

(b) placing the resulting first-wire-coiled mandrel parallel to and in contact with a second mandrel having a predetermined diameter;

(c) yoverwinding a second wire of predetermined fine diameter as a coil of predetermined high pitch completely about said first-Wire-coiled mandrel and said parallel second mandrel to form an overwound composite;

(d) winding said overwound composite as a coil of predetermined pitch about a third mandrel of predetermined large diameter;

(e) coiling on a fourth mandrel said overwound composite as coiled on said third mandrel;

(f) withdrawing said fourth mandrel from the coil formed thereover;

(g) setting the resulting triple coil by heating same in in a non-oxidizing atmosphere at a predetermined temperature for a predetermined time; and

(h) dissolving said first mandrel and said third mandrel while leaving said first wire coil engaging both said second mandrel and said second wire coil to hold second wire coil in position on said second mandrel.

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS 7/ 1959 Canada. 6/ 1948 Great Britain.

CHARLES W. LANHAM, Primary Examiner.

DAVID J. GALEN, Examiner. Q5 A. J. JAMES, W. JUST, Assistant Examiners, 

1. THE METHOD OF MAKING A COILED WIRE AND MANDREL SUITABLE FOR USE AS AN ELECTRODE COIL FOR AN ELECTRIC DISCHARGE DEVICE, WHICH METHOD COMPRISES: (A) WINDING A FIRST WIRE AS A COIL ABOUT A FIRST MANDREL; (B) PLACING THE RESULTING FIRST-WIRE-COILED MANDREL PARALLEL TO AND ADJACENT A SECOND MANDREL; (C) OVERWINDING A SECOND WIRE AS A COIL COMPLETELY ABOUT SAID FIRST-WIRE-COILED MANDREL AND SAID PARALLEL AND ADJACENT SECOND MANDREL TO FORM AN OVERWOUND COMPOSITE; AND (D) WHEN SAID OVERWOUND COMPOSITE IS IN ITS DESIRED ELECTRODE COIL CONFIGURATION, REMOVING SAID FIRST MANDREL WHILE LEAVING SAID FIRST WIRE COIL TO HOLD SAID SECOND WIRE COIL IN POSITION ABOUT SAID SECOND MANDREL. 